The present invention relates to an imaging device and a method of processing an imaging result in an imaging device, and can be applied to an electronic still camera for example. The invention employs a three-dimensional look-up table and corrects an imaging result by use of the three-dimensional look-up table, to thereby enable image quality to be readily and flexibly corrected, with the deterioration of the image quality being avoided effectively.
Conventionally, there has been provided an electronic still camera that allows image quality to be variously set according to color mode selection, and thus can offer wide compatibility with imaging environments, user's preferences, etc.
Specifically, in this kind of electronic still camera, image data obtained by an imaging element is subjected to auto white balance adjustment, grayscale correction, and chroma correction, followed by being recorded in a memory card as a recording medium in a format compatible with DCF (Design rule for Camera File System). In the setting of image quality according to the color mode selection, the settings of the grayscale correction and chroma correction are switched.
The grayscale correction is to correct grayscales of image data defined by red, green and blue (RGB) with use of a nonlinear function. In the grayscale correction, e.g., the sense of brightness and the sense of contrast of image quality are operated in order to bring the contrast of an imaging result close to that of actual look of the imaged object. Various configurations relating to the correction have been proposed in e.g., Japanese Patent Laid-open No. 2004-104464. When image quality is set based on a color mode, parameters defining the nonlinear function are changed in the grayscale correction.
In contrast, the chroma correction is processing in which image data based on RGB is converted into image data based on a luminance signal and color difference signals, and then the image data based on a luminance signal and color difference signals is linearly transformed on a color difference plane defined by color difference signals. The chroma correction is applied to tint adjustment and chroma adjustment in which chroma is increased to offer impressive image quality or is decreased to prevent grayscale error. When image quality is set based on a color mode, parameters defining the linear transformation processing are changed in the chroma correction.
Therefore, in an electronic still camera, plural kinds of two groups of parameters relating to the grayscale correction and chroma correction are prepared and recorded according to imaging environments and user's preferences. The selection of a color mode at the time of imaging leads to setting of the corresponding parameters.
However, the processing for adjusting image quality through the grayscale correction and chroma correction problematically involves inadequacy in terms of practical use.
Specifically, when chroma correction is implemented by linear transformation on a color difference plane as described above, lightness is also changed, which problematically deteriorates image quality. This problem is elicited by chroma enhancement accompanied by the corresponding lightness increase. More specifically, although a change of the level of a color difference signal causes no change of a luminance signal, this level change of the color difference signal in the L*a*b* color system, which is a color system close to the perception of a human, problematically leads to a change of the lightness L*. When the gain of a color difference signal is increased by the chroma correction, the lightness L* increases in an area with a high chroma and a low lightness, which spoils the three-dimensional appearance of the imaging result.
As one method to address this problem, a method is possible in which chroma correction is carried out through 3×3 matrix arithmetic of image data made up of red, green and blue signals. However, even this method cannot prevent a change of lightness completely.
In addition, there is another problem that the grayscale correction and chroma correction are processing for converting the entire color space, and therefore involve a difficulty in adjusting only a limited area of the color space. Accordingly, flexible correction of image quality is impossible. For example, adjusting the tint of the red region leads to an unnatural skin color, and operating the tint of the yellow region affects the green region. As a result, adjustment operations for the respective representative colors have an effect on each other, and therefore adequate adjustment of all the representative colors is impossible.
Furthermore, there is also a problem that, although the color space includes both a color that is readily saturated and a color that has a reduced tendency of being saturated, the grayscale correction and chroma correction cannot offer processing in which the existence of these opposite colors is taken into consideration, and thus readily cause the deterioration of image quality due to the color saturation.
As one method to solve, of the above-described problems, the problem relating to the flexibility, a method has been proposed in which a color space to be used in chroma correction is divided into plural areas and processing is executed in the respective divided areas. However, even by this method, a mutual effect between colors having similar hues, such as red and a skin color, and yellow and green, cannot be prevented in practice.
Therefore, these problems arise not only when image quality is adjusted based on a color mode, but necessarily arise when grayscale correction such as gamma correction and chroma correction are executed in an electronic still camera.
As a method to solve these problems collectively, there is a method in which imaging results are recorded and held as files and then are down-loaded to a computer, followed by being subjected to edit processing. However, this method forces a user to implement troublesome operations, and therefore all users cannot use this method easily.